This invention is generally directed to processes for the preparation of electron transporting compounds, and more specifically the present invention is directed to specific processes for obtaining anthraquinodimethane derivatives and related anthrone derivatives. Therefore, in one embodiment of the present invention there are prepared anthraquinone and anthrone derivatives by the reaction of an anthraquinodimethane with active methylene compounds, inclusive of malononitrile, in a suitable organic solvent, which reaction is accomplished in the presence of a base and a Lewis acid. The resulting anthraquinodimethane derivatives and related anthrone derivatives are useful as electron transporting compounds in imaging members containing therein a photogenerating layer. These imaging members are the claimed subject matter of a copending application U.S. Ser. No. 709,867 entitled Photoresponsive Imaging Members With Electron Transporting Layers, the disclosure of this copending application being totally incorporated herein by reference.
The generation and development of electrostatic latent images on the surfaces of photoconductive materials by electrostatic means is well known. One electrostatic method involves the formation of a latent image on the surface of a photosensitive plate, or a photoreceptor. These photoreceptors can be comprised of a conductive substrate containing on its surface a layer of photoconductive insulating material, and in many instances there can be incorporated therein a thin barrier layer between the substrate and the photoconductive layer to prevent charge injection into the photoconductive layer upon charging of its surface, which injection would adversely affect the quality of the resulting image.
Numerous different xerographic photoconductive members are known including, for example, a homogeneous layer of a single material such as vitreous selenium, or composite layered devices, with a photoconductive substance dispersed in other substances. An example of one type of composite photoconductive layer used in xerography is described, for example, in U.S. Pat. No. 3,121,006 wherein there is disclosed a number of layers comprising finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. In a commercial form, the binder layer contains particles of zinc oxide uniformly dispersed therein and coated on a paper backing. The binder materials disclosed in this patent comprise a material which is incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. Accordingly, as a result the photoconductive particles must be in a substantially contiguous particle to particle contact throughout the layer for the purpose of permitting charge dissipation required for a cyclic operation. Illustrative examples of specific binder materials disclosed in this patent include, for example, polycarbonate resins, polyester resins, polyamide resins and the like.
There are also known photoreceptor materials comprised of other inorganic or organic materials wherein the charge carrier generation and charge carrier transport functions are accomplished by discrete contiguous layers. Additionally, photoreceptors are disclosed in the prior art which include an overcoating layer of an electrically insulating polymeric material and in conjunction with this overcoated type photoreceptor there have been proposed a number of imaging methods. However, the art of xerography continues to advance and more stringent demands need to be met by the copying apparatus for increased performance. Additionally, positively charged layered photoresponsive imaging members are needed for generating images of acceptable resolution, and substantially no undesirable background deposits.
Recently, there has been disclosed layered photoresponsive devices comprised of generating layers and hole transport layers, reference U.S. Pat. No. 4,265,990, and overcoated photoresponsive materials with a conductive layer, overcoated with a hole transport layer followed by an overcoating of a photogenerating layer and a top coating of an insulating organic resin, reference U.S. Pat. No. 4,251,612. Examples of generating layers disclosed in these patents include trigonal selenium and phthalocyanines, while examples of the active transport layer molecules that may be employed are comprised of certain diamines as mentioned herein. The disclosures of each of these patents, namely U.S. Pat. Nos. 4,265,990 and 4,251,612, are totally incorporated herein by reference.
Many other patents are in existence describing layered photoresponsive devices with generating pigments such as U.S. Pat. No. 3,041,167, which discloses an electrophotographic imaging process employing an overcoated imaging member containing a conductive substrate, a photoconductive insulating layer, and an overcoating layer of an electrically insulating polymeric material. This member is utilized in an electrophotographic copying method by, for example, initially charging the member with an electrostatic charge of a first polarity and imagewise exposing to form an electrostatic latent image which can be subsequently developed to form a visible image. Prior to each succeeding imaging cycle, the member can be charged with an electrostatic charge of a second polarity which is opposite in polarity to the first polarity. Sufficient additional charges of the second polarity are applied so as to create across the member a net electrical field of the second polarity. Simultaneously, mobile charges of the first polarity are created in the photoconductive layer such as by applying an electrical potential to the conductive substrate. The imaging potential which is developed to form the visible image is present across the photoconductive layer and the overcoating layer.
Other representative prior art disclosing layered photoresponsive devices include U.S. Pat. Nos. 4,115,116; 4,047,949; 4,081,274 and 4,315,981. According to the disclosure of the '981 patent, the recording member consists of an electroconductive support, a photoconductive layer of organic materials which contain a charge carrier producing dyestuff layer of a compound having an aromatic, or heterocyclic polynuclear quinone ring system, and a charge transport layer.
Furthermore, there is disclosed in U.S. Pat. No. 4,135,928 electrophotographic light sensitive members comprised of 7-nitro-2-aza-9-fluroenylidene-malononitrile as charge transporting substances. According to the disclosure of this patent, the electrophotograhic light sensitive members are comprised of an electroconductive support, a layer thereover of a photogenerating substance, and 7-nitro-2-aza-9-fluorenylidene-malononitrile of the formula, for example, as illustrated in column 1.
There is also disclosed in U.S. Pat. No. 4,474,865 imaging members with electron transporting layers of fluorenylidene derivatives. These electron transporting compounds differ from those of the present invention in that they are based on the fluorenone structure with a 5-member central ring; while the transporting compounds of the present invention are based on anthrone and anthraquinone structures which contain a 6-member central ring. In addition, while the fluorenylidene derivatives are relatively planar in structure, the anthrone and anthraquinone derivatives of the present invention are buckled and assume a butterfly-like conformation.
While the above-described photoresponsive imaging members are suitable for their intended purposes there continues to be a need for improved imaging members, particularly layered imaging members, which not only generate acceptable images but which can be repeatedly used in a number of imaging cycles without deterioration thereof from the machine environment or surrounding conditions. Additionally, there continues to be a need for improved layered photoconductive imaging members wherein the materials selected are substantially inert to users of these members. Also, there continues to be a need for positively charged imaging members with electron transporting compounds. Additionally, there continues to be a need for improved photoresponsive imaging members which can be prepared with a minimum number of processing steps, and wherein the layers are sufficiently adhered to one another to allow the continuous use of these members in imaging and printing processes.
Also, there is a need for electron transport compounds which are compatible with common matrix polymers, inclusive of polycarbonates, and polyesters enabling the dispersion of these compounds to be maintained for the useful life of the layered imaging members. Moreover, there continues to be a need for a simple synthetic process for the preparation of anthrone, and anthraquinodimethane electron transporting compounds.